Fibromyalgia, a chronic musculoskeletal pain disorder of unknown etiology, is a significant public health problem. Evidence from studies of phenomenology, comorbidity, family history, and pharmacologic treatment response suggest that fibromyalgia may be associated with major mood disorder, and possibly to a proposed group of conditions known as affective spectrum disorders. Prior psychiatric research has demonstrated that major mood disorder is highly familial. Family history studies provide a method by which to assess how medical disorders co-aggregate in families and, therefore may share a common risk factor or pathophysiologic mechanism. To date, few studies have explored the morbid risk of major mood disorder (and other proposed affective spectrum disorders) in probands with fibromyalgia and their first- degree relatives. All of these studies have used the family history method, which entails interviewing probands regarding their knowledge of psychiatric illness in relatives. Although most of these studies have provided important preliminary data suggesting an association between fibromyalgia and major mood disorder, this method has been demonstrated to be less sensitive in detecting illness in relatives than direct interview (the family interview method). In order to provide further evidence of a relationship between fibromyalgia and major mood disorder, we propose to study the prevalence of psychiatric and rheumatologic disorders in probands with fibromyalgia and their first-degree relatives as compared to probands with rheumatoid arthritis and their relatives using the family interview method. In addition to assessing the degree of co-aggregation of these disorders within families, we will also study the occurrence of other conditions within the proposed group of affective spectrum disorders in relation to fibromyalgia, and the association between the severity of fibromyalgia symptoms and the presence of major mood disorder within families.